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Ash dieback disease

Ash Dieback disease

Information and advice on ash dieback disease, also known as Chalara fraxinea, which is a potentially serious threat to ash trees across the UK.


  • there is no need to fell ash trees unless Chalara is confirmed in the tree, and the precautionary felling of trees is not recommended at this time

  • only purchase trees from reputable suppliers and make sure that they are certified disease free stock

  • anyone concerned by a possible case should approach (1) the owner of the tree concerned and (2) the government helpline on 03459 335577

  • the disease does not give any exemptions from legal requirements to seek permission to do works to protected trees, and to give notice of any works to trees in conservation areas. If you need advice on whether your tree is protected please contact your local council's tree protection department

Frequently Asked Questions


What is Ash dieback?

Ash dieback is caused by a fungal organism called Chalara fraxinea. The disease causes leaf loss and crown dieback in affected trees, and can lead to tree death. The fungal disease is carried on the wind and by transportation of infected trees.

Which Ash trees are at risk?

All ash trees are vulnerable; it is not known to spread to any other type of tree. It is particularly destructive to young trees. Older trees can survive initial attacks, but tend to succumb eventually after several seasons of infection

The disease does not cause rapid or catastrophic failure of trees. Any danger from dead or dying trees is likely to be gradual and obvious over a period of year. Chalara fraxinea is not fatal to all ash trees. The older infected trees may be able to survive indefinitely, although may be at increased risk of other infections

Further information can be obtained via  Forestry Commission - Chalara information (opens in a new window)

How serious is Ash Dieback?

The disease is a potentially serious threat to ash trees across the UK.

Ash Dieback (Chalara fraxinea) is a new disease affecting ash trees (Fraxinus sp.) and has recently been found in Britain.

The disease has already caused extensive loss of ash trees in mainland Europe, and could be a major threat to wild and planted ash in the UK if it takes hold here.
Chalara dieback of ash, caused by the fungus Chalara fraxinea, was found in the UK for the first time in early 2012 in young ash plants in tree nurseries and recently planted sites, including a car park, a college campus, and a new woodland.

The disease has not yet been found in the South West.

From Monday October 29, 2012, the government has implemented a ban on the import of ash plants into the UK and on the movement of ash plants, seeds and trees into and around the UK. The ban does not extend to the movement of ash timber or firewood except from sites where the disease has already been found.

What are the signs of the disease?

The disease is is not always easy to identify so check Forestry Commission - Chalara information (opens in a new window) for videos and guides which explain the symptoms and identification of the disease.

It is characterised by the premature loss of leaves from the outer parts of the crown (top and sides), accompanied by long diamond-shaped lesions or areas of sunken and discoloured bark on twigs.

These lesions girdle twigs and small branches, starving the leaves above of water and nutrients and causing whole branches to die. In mature trees, it is the new growth that is affected.

Video showing how to identify ash dieback disease by the Food and Environment Research Agency (FERA) (opens in a new window)

Diagnostic guide to the symptoms of Chalara (pdf, 281kb) (opens in a new window) by the Forestry Commission

Because one of the symptoms of Chalara fraxinea is leaf loss, identification of the disease will be difficult in the autumn when the trees are losing their leaves.

What should I do if I think I have found Chalara disease?

The disease has been classified as 'notifiable' by DEFRA, which means that any suspected cases of the disease must be reported to the appropriate plant health authorities.

If you think that you have identified Chalara fraxinea on an ash tree, then you should contact one of the following bodies:

Government national Ash Dieback disease helpline:

Tel: 03459 335577 (8am - 6pm daily)

Forest Research Disease Diagnostic Advisory Service

Tel: 01420 23000


Forestry Commission Plant Health Service

Tel: 0131 314 6414


FERA Plant Health and Seeds Inspectorate

Tel: 01904 465625


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